1. Field of the Invention
The present invention relates to a floppy disk control circuit that controls a spindle motor drive circuit that drives a spindle motor to rotate a floppy disk and a floppy disk apparatus having such a floppy disk control circuit.
2. Description of the Related Art
In recent years, floppy disk apparatus that use a USB (Universal Serial Bus) interface instead of the conventional legacy interface as the interface with a host apparatus, such as a personal computer, have become available as commercial products. Such known floppy disk apparatuses are disclosed in for example Laid-open Japanese Patent Application No. H. 11-306501, Laid-open Japanese Patent Application No. 2000-311422 and Laid-open Japanese Patent Application No. 2002-74810. The basic configuration of such known floppy disk apparatuses is as shown in FIG. 4. Specifically, such a floppy disk apparatus 1 includes an interface control circuit 10 that communicates with the host apparatus 2 through a USB, a floppy disk control circuit 11 that receives control data or write data from the interface control circuit 10 or sends read data to the interface control circuit 10 and that controls a spindle motor drive circuit 12, a stepping motor drive circuit 14 and a read/write circuit 16 (described subsequently), a spindle motor drive circuit 12 that is controlled by the floppy disk control circuit 11, a spindle motor 13 that is driven by the spindle motor drive circuit 12 so as to rotate the floppy disk, a stepping motor drive circuit 14 that is controlled by the floppy disk control circuit 11, a stepping motor 15 that shifts a magnetic head 17 (described subsequently), driven by the stepping motor drive circuit 14, a read/write circuit 16 that performs input/output of read and write data with the floppy disk control circuit 11 and performs input/output of electrical signals with respect to a magnetic head 17, and a magnetic head 17 that converts magnetic signals on the floppy disk to electrical signals or converts electrical signals to magnetic signals.
Recently, space-saving and/or cost-reduction are performed by using a semiconductor integrated circuit (hereinbelow referred to as a three-in-one chip) 9 that integrates the three main circuits of the floppy disk control circuit 11, stepping motor drive circuit 14 and read/write circuit 16. This three-in-one chip 9 is a custom product which must be customized for each customer with respect to, for example, the transfer rate of the read/write circuit 16. In contrast, a standard semiconductor integrated circuit is typically used for the spindle motor drive circuit 12.
With commercialization of such USB interface floppy disk apparatuses, it has become possible to increase the read/write speed of floppy disks, which was restricted by the legacy interface.
However, the standard for an apparatus using a USB interface restricts the maximum allowed current to no more than 500 mA. Specifically, if the current value exceeds this, source current may not be supplied from, for example, the host apparatus 2 because the host apparatus 2 regards such an apparatus as unsuitable. In the development of a three-in-one chip for controlling a standard spindle motor drive circuit for application to a floppy disk apparatus capable of reading/writing with double or quadruple speed, the inventor of the present application recognized that this maximum allowed current posed a problem during the start-up of rotation of the floppy disk. More specifically, when the floppy disk of such a double or quadruple speed floppy disk apparatus is rotated at a steady speed, the current consumption is below the maximum allowed current. However, the inventor found that, since the spindle motor requires a large torque during start-up of rotation, as shown in FIG. 5, this current consumption ICC exceeds the maximum allowed current and in fact increases to the vicinity of 1A. The character t0, which has a value of, for example, 500 mS) in FIG. 5 is the time at which read/write operation and other operations of the floppy disk apparatus actually commence.